#6 and #8 Screw Torques

briand · #1 11-01-2006, 02:07 PM

I've been waiting to tighten the million screws that attach my tanks until I got a torque screw driver so today I ordered one and can't seem to find these torque limits anywhere.

My Standard Aircraft Handbook (where I expected to find them) only lists down to an 8-32 bolt (12-15 in-lbs.) which is prabably the same as a #8 screw but I'm not positive.

az_gila · #2 11-01-2006, 04:43 PM

Depends on the material the #8 screw is made from....

Which part number are you using?

gil in Tucson

briand · #3 11-01-2006, 05:58 PM

AN509-8R8
AN507-6R6

az_gila · #4 11-01-2006, 11:11 PM

For the AN509-8, which are made from 125,000 psi steel, my Airframe Mechanics book shows 12 to 15 inch-lbs. - they are treated like the bolts you mention in your previous post.

I don't have a #6 torque reference, but the AN507 screws are made from only 55,000 psi steel, and would be much less.
If they were AN507 at #8 size, I would expect about 5 to 7 inch-lbs. based on the material. The AN507 are not really considered structural...

gil in Tucson

cytoxin · #5 11-02-2006, 05:12 AM

wow thats a little bit..tighten them down till they clamp then give em a bump.

briand · #6 11-02-2006, 07:56 AM

Don't tell me that. I just spent $50 on a torque screwdriver.

cytoxin · #7 11-02-2006, 07:59 AM

Quote:

Originally Posted by briand

Don't tell me that. I just spent $50 on a torque screwdriver.

ok i take it back..and dont forget to add drag torque to the 12-15 or you may never even get it started

az_gila · #8 11-02-2006, 11:09 AM

I went and talked to our Mechanical designers at work and they pointed me to this table... small portion copied here....

Screw Size .138-32 (#6)

Lubricated Screw Threads 12 in-lb.

Dry Non-Locking Threads 14 in-lb.

Dry Locking Threads 16 in-lb.

Screw Tensile Stress Area (sq. in) 0.00909

This is for 80,000 psi material... scale it down for the AN507 55,000 psi screws, or use better screws...

Also note that these numbers include an allowanace for the friction drag, don't add extra....

I guess they don't want the assembly people doing mathematical calculations.

These numbers are good for unmanned, guided, high speed aerospace vehicles.... should be good enough for our RVs....

Test first....

Data is derived from M. F. Spotts, Design of Machine Elements and Mechanical Engineering Design by Joseph Shigley.

gil in Tucson